This disclosure relates to stable, high activity platinum alloy catalysts for use in fuel cells or other catalyst applications.
Fuel cells are commonly used for generating electric current. For example, a single fuel cell typically includes an anode catalyst, a cathode catalyst, and an electrolyte between the anode and cathode catalysts, for generating an electric current in a known electrochemical reaction between a fuel and an oxidant.
One issue encountered with fuel cells is the operational efficiency of the catalysts. For example, electrochemical activity at the cathode catalyst is one parameter that controls the efficiency. An indication of the electrochemical activity is the rate of electrochemical reduction of the oxidant at the cathode catalyst. Platinum has been used for the cathode catalyst. However, platinum is expensive and has a high over-potential for the cathodic oxygen reduction reaction. Also, platinum is relatively unstable in the harsh environment of the fuel cell. For instance, elevated temperatures and potential cycling may cause degradation of the electrochemical activity of the platinum over time due to catalyst dissolution and particle migration.
Platinum has been alloyed with certain transition metals to increase the catalytic activity and provide greater stability. Even so, the catalytic activity and stability for a given alloy composition depends to a considerable degree on the technique used to fabricate the alloy. As an example, some techniques may produce relatively large catalyst particle sizes and poor dispersion of the alloying elements, which may yield poor electrochemical activity in a fuel cell environment, despite the alloy composition.